1. Field of the Invention
The present invention relates to a device which detects a shake of a camera to prevent the shake.
2. Related Background Art
An optical detection method and a mechanical detection method have been known to detect camera shake.
In the optical detection method, a two-dimension image sensor or a plurality of one-dimension image sensors are used to detect a positional displacement of an object image by the shake.
The mechanical detection method includes an acceleration detection method in which an acceleration of the shake when a camera body is shaked is detected to calculate the positional displacement of the object image based on the acceleration, and an angular velocity detection method in which an angular velocity of the shake when the camera body is shaked is detected to calculate the positional displacement of the object image based on the angular velocity.
When the optical shake detection method is applied to the camera, it is necessary in a one-eye reflex type camera to drive a mirror up immediately before a photograph is taken so that all lights through an objective lens are directed to a film when the photograph is taken. As a result, in the optical shake detection method, the shake can be detected until immediately before the photographing but cannot be detected during the photographing.
When the mechanical shake detection method is applied to the camera, in the acceleration detection method, the shake cannot be detected during a constant velocity motion even if the shake is large, because it detects only the acceleration. Further, if a period of shake is long (a frequency of shake is low), the acceleration is low even if the shake is large, and the detected acceleration is small and detection error is large.
In the angular velocity detection method, a high precision gyroscope (for example, a laser gyroscope) used as a detector is large in size and expensive, and an inexpensive one is of low precision and difficult to determine if the velocity is zero or not. Further, when the period of shake is long (the frequency of shake is low), the angular velocity is low even if the shake is large, and the detected velocity is low and the detection error is large.
And in the conventional apparatus for detecting an unintentional movement of hands as shown in FIG. 11, an angular velocity sensor 201 detects angular velocity of a camera, a low-pass filter (hereinafter referred as "LPF") 202 filters off the high frequency components other than the unintentional movement of hands, and further a high-pass filter (hereinafter referred as "HPF") 203 consisting of a condenser C and a resistance R filters off the low frequency components other than the unintentional movement of hands including the direct current components. The output of the HPF 203 is amplified by a non-inverting type operational amplifier 204 and applied to an A/D conversion input terminal 205a of a control circuit 205 including a computer.
A connection point between the condenser C and the resistance R, which constitute the HPF 203, is connected with one terminal of a switch 206, while the other terminal of the switch 206 is earthed. The switch 206 is controlled, that is, turned on/off, according to a control signal output from a control terminal 205b of the control circuit 205.
In this constitution, when the power source (not shown) is turned on, the switch 206 is turned on to earth the connection point between the condenser C and the resistance R, thereby initializing the HPF 203. As the output of the non-inverting type operational amplifier 204 is arranged to be equal to 0 when the input value is 0, the output becomes equal to 0 V when the switch 206 is turned off.
The output of the angular velocity sensor 201 becomes static only some time after the power source is turned on, when the angular velocity can be detected. Therefore, after a predetermined time elapses, a control signal is output from the control terminal 205b of the control circuit 205 in order to turn off the switch 206 and bring the HPF 203 into the active state. Thus, a signal of the angular velocity of the unintentional movement of hands is output from the operational amplifier 204. Said signal is converted in the control circuit 205 into a digital signal in order to calculate the amount of the movement of hands.
FIGS. 12A to 12D are views showing waveforms obtained in respective units after the time (t=t0) when the power source is turned on, wherein the camera is shaken with the movement of hands. FIG. 12A shows the angular displacement, which is obtained by the angular velocity sensor 201, caused by the movement of hands. FIG. 12B shows the angular velocity v of the movement of hands, which is obtained as the output of the angular velocity sensor 201. FIG. 12C shows the output S of the LPF 202 and FIG. 12D shows the output OUT of the operational amplifier. Note that, in FIG. 12C, the broken line indicates the state without the movement of hands.
By the way, if the angular displacement .omega. caused by the movement of hands is represented as a sine wave as shown in FIG. 12A, the phase of the angular velocity v should be shifted theoretically from that of the angular displacement .omega. by 90.degree., as shown in FIG. 12B. In fact, however, only after the time (t=t1) for the angular velocity sensor to obtain stationary state elapses, the output of the angular velocity sensor 201 begins to correspond to the actual angular velocity, as shown in FIG. 12C.
When the switch 206 is turned off at time t2, when the time required for the angular velocity sensor 201 to obtain stationary state has already elapsed, the output OUT of the operational amplifier 204 at the time t2 is equal to 0 V. On the other hand, the output S of the LPF 202 is equal to 0 when there is no movement of hands, but becomes equal to the angular velocity .DELTA. v of the movement of hands when the movement thereof exists. Accordingly, when the movement of hands exists, the angular velocity v at the moment the switch 206 is turned off can not be obtained according to the output OUT of the operational amplifier 204.
More specifically, the angular velocity v when the movement of hands exists, which is indicated by the broken line in FIG. 12D, can be expressed as follows: EQU .DELTA. v 1-EXP{-(t-t2)/CR}!
If the angular velocity at the time when the output OUT of the operational amplifier 204 is equal to 0 V, the value of the error is obtained according to the above expression. Therefore, the greater the angular velocity .DELTA. v of the movement of hands when the switch 206 is turned off becomes, the longer the time T until the operational amplifier 204 outputs the exact angular velocity v becomes, which is troublesome.